The development of a safe and effective HIV-1 vaccine is a global health priority. Recombinant adenovirus serotype 5 (rAd5) vector-based vaccines have been shown to elicit potent cellular immune responses in animal models and are being developed as candidate HIV-1 vaccines. However, the high prevalence of preexisting immunity to Ad5 in human populations will likely substantially limit the immunogenicity and clinical utility of rAd5 vaccines. Recombinant adenovirus serotype 35 (rAd35) vector-based vaccines are therefore being developed as potential alternatives to rAd5 vaccines. Our preliminary studies demonstrate that a rAd35-Gag vaccine effectively evades anti-Ad5 immunity but is substantially less immunogenic than a rAd5-Gag vaccine in mice. The development of improved vaccine vectors is therefore urgently needed. [unreadable] [unreadable] In this Innovation Grant, we propose to construct novel chimeric rAd vectors that combine the desirable properties of rAd5 and rAd35. The Ad5 fiber protein may be critical for rAd5 immunogenicity, whereas the Ad5 hexon protein is the primary target of Ad5-specific neutralizing antibodies. We therefore hypothesize that chimeric rAd vectors containing the Ad5 fiber and the Ad35 hexon will both retain the immunogenicity of rAd5 and effectively evade anti-Ad5 immunity. If successful, these novel vectors could be developed rapidly as improved adenovirus vaccines for HIV-1. We propose the following three Specific Aims: [unreadable] [unreadable] I. To construct and assess the immunogenicity of rAd35 vectors containing the Ad5 fiber in mice; [unreadable] II. To construct and assess the immunogenicity of rAd5 vectors containing the Ad35 hexon in mice; and [unreadable] III. To assess the immunogenicity of the optimal chimeric rAd vector in a pilot study in rhesus monkeys. [unreadable] [unreadable] This project is consistent with the goals of PA-03-082, which aims to support the entrance of innovative, exploratory, high risk/high impact prophylactic vaccine concepts into the research pipeline. Within the two-year time frame of this award, sufficient data will be generated with candidate chimeric rAd vaccines to justify further vaccine/challenge studies in rhesus monkeys. [unreadable] [unreadable]